The invention relates to an exposure mask with a measuring wheel and a switching means to control a transport unit for photographic material.
In previously proposed transport units for photographic paper, for example, in photographic roll printing apparatus, the transport distance by which the paper is advanced at the end of each printing operation is measured by means of a measuring wheel attached to a paper mask. The measuring wheel acts on a switching means, for example, a micro-switch, by way of a transmission member, in such a way that a paper transport motor switched on at the start of the transport is switched off after a number of rotations of the measuring wheel corresponding to the desired transport distance. The diameter of the measuring wheel and the transmission member, which may for example contain a gear, are so matched to each other that the transport distance is suitable for the dimensions of the light passage aperture of the paper mask, and therefore the print size which is to produced. In such previously proposed roll printing apparatus, therefore, a separate mask with a separate transport measuring device, which in each case contains a measuring wheel, is required for each print size. As a result, the user of such apparatus must acquire for each print size required a paper mask which is relatively expensive, particularly owing to the cost of the transport measuring device, but many of these masks, for example, a mask for exposing test strips, are used relatively rarely.